The present invention relates to an optical disc recording apparatus which can form an image on an optical disc, and a method of forming an image on an optical disc.
Optical discs such as a CD-R (Compact Disc Recordable) or a CD-RW (Compact Disc Rewritable) are widely used for recording large volumes of information. An optical disc recording apparatus records information such as music data by applying a laser beam to a recording place which is formed in one face of an optical disc.
An image such as characters indicating a title, symbols, and the like is formed on a label face (opposite to the recording face) of the optical disc, thereby enabling data recorded in the recording face to be identified. Such an image is formed by printing it onto a label sheet with using a printing apparatus or the like, and then applying the label sheet to the label face of the optical disc.
Therefore, such a formation of an image on an optical disc requires a printing apparatus in addition to an optical disc recording apparatus. Furthermore, a troublesome work of applying a label sheet onto which an image is printed to an optical disc is necessary.
In order to solve the problems, an optical disc recording apparatus has been proposed which has a function of forming an image such as title characters on a label face or recording face of an optical disc as shown in FIG. 14 (hereinafter, referred to as drawing function), in addition to a function of recording information such as music data onto the optical disc (hereinafter, referred to as information recording function).
At present, as an optical disc recording apparatus which can realize the drawing function, proposed are an optical disc recording apparatus of the CLV (Constant Linear Velocity) system in which recording is performed while controlling the power of a laser beam emitted from an optical pickup to an optical disc to be constant, and changing the rotation number of a spindle motor that rotates the optical disc, and that of the CAV (Constant Angular Velocity) system in which recording is performed while controlling the rotation number of a spindle motor to be constant, and changing the power of a laser beam emitted from an optical pickup to the optical disc. Such optical disc recording apparatuses have the following problems.
In an optical disc recording apparatus of the CLV system, as described above, an image is formed on an optical disc while changing the rotation number of a spindle motor. In the case where address information specifying the laser beam irradiation position (i.e., the radial position of an optical pickup on the optical disc) is previously recorded on the optical disc, the address information can be reproduced so that the radial position of the optical pickup can be determined, thereby enabling a stable rotation control on the spindle motor (hereinafter, referred to as spindle servo).
In the case where address information is not previously recorded on the optical disc, such as the case where an image is to be formed on the label face of the optical disc, however, the radial position of the optical pickup cannot be determined, with the result that the spindle servo is unstable.
In such a case, the spindle servo is conducted on the basis of an FG (Frequency Generator) signal supplied from a rotation detector attached to the spindle motor, i.e., a pulse signal in which the pulse generation period is changed in accordance with the rotation speed (the rotation number per unit time) of the spindle motor. However, the FG signal involves a large error, and hence is not suitable for the spindle servo in which the rotation number of the spindle motor is continuously changed. The spindle servo affects the writing quality. When the spindle servo is not stabilized, consequently, there arises a problem in that the quality of an image to be formed on the optical disc is lowered.
By contrast, in an optical disc recording apparatus of the CAV system, as described above, an image is formed on an optical disc while maintaining the rotation number of a spindle motor and changing the laser power. Therefore, the spindle servo can be performed more stably than that in the case of an optical disc recording apparatus of the CLV system. When the rotation number of the spindle motor is controlled so as to be constant, the linear velocity of the inner peripheral side of the optical disc is lower than that of the outer peripheral side. In order to form an image of a density which is uniform over a substantially whole area of the optical disc, therefore, the power of a laser beam irradiated onto the inner peripheral side of the optical disc must be set to be lower than that of a laser beam irradiated onto the outer peripheral side. Namely, the formation of an image of a uniform density over a substantially whole area of the optical disc requires complex and troublesome works such as that of obtaining an optimum laser power on the basis of the radial position of the optical pickup.